An Al-Si alloy brazing filler metal for brazing 5000 series aluminum alloys and its preparation method

Abstract

The present invention discloses an Al-Si alloy filler metal for brazing 5000 series aluminum alloys and a preparation method thereof. During the process of using the Al-Si alloy filler metal for brazing 5000 series aluminum alloys, the Mg element in the base metal diffuses into the filler metal and reacts with Si in the filler metal to form the Mg<subgt;2< / subgt;Si phase, and its morphology and distribution affect the performance of the brazed joint. The combined addition of Be and Sb can improve the morphology of Mg<subgt;2< / subgt;Si. The Sb element and the Mg element diffused into the reaction zone combine to form Mg<subgt;3< / subgt;Sb<subgt;2< / subgt> particles, providing nucleation sites for the crystallization of the Mg2Si phase and reducing the size of the Mg<subgt;2< / subgt>Si phase. After adding the Be element, Be tends to adsorb on the {100} crystal plane of the Mg<subgt;2< / subgt>Si phase and combines with Mg atoms, inhibiting the growth of the Mg<subgt;2< / subgt>Si phase along the <100> crystal direction, making Mg

Description

Technical Field

[0001] The present invention belongs to the field of new materials, and particularly relates to an Al-Si alloy solder foil for brazing 5000 series aluminum alloys, which has a low melting point, good wettability, can improve the microstructure of the brazed joint and enhance the joint strength, and a preparation method thereof. Background Art

[0002] Due to its high specific strength, excellent corrosion resistance, workability and thermal conductivity, aluminum-magnesium alloy is widely used in fields such as ship structures and offshore facilities, automobiles, high-speed trains, aerospace, transport tanks and pressure vessels, which have certain requirements for corrosion resistance, weldability and static strength. Brazing has become a widely used welding method for aluminum alloys due to its advantages such as small welding stress and deformation, ability to weld dissimilar metals, and high production efficiency. However, the problems of low strength of the brazed joint and high-temperature softening have always hindered the application of aluminum-magnesium alloy.

[0003] Aluminum alloy brazing generally uses Al-Si series solder, which has good wettability, fluidity and corrosion resistance. However, the melting point of Al-Si series solder is relatively high (the Al-Si eutectic temperature is 577 °C), and the brazing temperature is generally between 600 °C and 615 °C, which is close to the solidus line of the aluminum alloy base material. Too high brazing temperature is extremely likely to cause the growth and softening of the grains of the aluminum alloy base material, and is also likely to cause defects such as overburning and corrosion of the base material, thereby reducing the performance of the brazed joint. At the same time, when using Al-Si solder to braze 5000 series aluminum alloys, acicular eutectic Si and fibrous Mg2Si phases will be generated in the brazing seam, increasing the brittleness at the brazing seam and making the joint extremely prone to fracture, and the performance of the brazed joint is poor.

[0004] In view of the current problems of high brazing temperature of Al-Si solder and poor performance of the brazed joint of 5000 series aluminum alloys due to the formation of brittle phases in the brazed joint, developing a low-temperature Al-Si alloy solder for brazing 5000 series aluminum alloys and being able to improve the phase morphology of the brazed joint at the same time is of great significance for improving the joint quality and application fields of aluminum-magnesium alloy brazing. Summary of the Invention

[0005] The purpose of the present invention is to overcome at least one deficiency of the prior art and provide an Al-Si alloy solder for brazing 5000 series aluminum alloys and a preparation method thereof.

[0006] The technical solution adopted by the present invention is:

[0007] In the first aspect of the present invention, it provides:

[0008] An Al-Si alloy solder, with its mass composition being: Si 11.0 - 13.0%, Zn 9.0 - 11.0%, Cu 0.80 - 1.30%, Cr 0.15 - 0.25%, Ni 0.15 - 0.20%, Mn 0.10 - 0.15%, Be 0.40 - 0.60%, Sb 0.20 - 0.30%, Ti 0.10 - 0.15%, and the balance being aluminum and unavoidable impurities.

[0009] In some examples of the Al-Si alloy solder, its mass composition is: Si 11.4 - 12.5%, Zn 10.0 - 11.0%, Cu 1.10 - 1.30%, Cr 0.20 - 0.25%, Ni 0.10 - 0.30%, Mn 0.10 - 0.15%, Be 0.42 - 0.55%, Sb 0.22 - 0.30%, Ti 0.10 - 0.15%, and the balance being aluminum and unavoidable impurities, and the content of the unavoidable impurities does not exceed 0.1%.

[0010] In some examples of the Al-Si alloy solder, the Be / Sb mass ratio is (1.7 - 2.3):1.

[0011] In some examples of the Al-Si alloy solder, the total mass fraction of Be + Sb is 0.60 - 0.90%.

[0012] In some examples of the Al-Si alloy solder, the Be / Sb mass ratio is (1.7 - 2.3):1, and the total mass fraction of Be + Sb is 0.60 - 0.90%.

[0013] In some examples of the Al-Si alloy solder, the content of the unavoidable impurities does not exceed 0.1%.

[0014] In some examples of the Al-Si alloy solder, the Be / Sb mass ratio is (1.7 - 2.3):1, and the content of the unavoidable impurities does not exceed 0.1%.

[0015] In some examples of the Al-Si alloy solder, the Be / Sb mass ratio is (1.7 - 2.3):1, the total mass fraction of Be + Sb is 0.60 - 0.90%, and the content of the unavoidable impurities does not exceed 0.1%.

[0016] The second aspect of the present invention provides:

[0017] A method for preparing the Al-Si alloy solder according to the first aspect of the present invention, comprising the following steps:

[0018] S1). Weigh the raw materials according to the composition ratio of the Al-Si alloy solder, clean and dry them for standby;

[0019] S2). Transfer the raw materials into a smelting furnace, heat and smelt them at a temperature of 730 - 760 °C, and stir evenly after slag removal;

[0020] S3). Add a refining agent, remove slag and let it stand for filtration after refining;

[0021] S4). Wait for the molten liquid to cool to 690 - 710 °C and pour it into a metal mold preheated to 200 - 250 °C to obtain an alloy ingot;

[0022] S5). Anneal the alloy ingot homogenously at 470 - 490 °C for 24 - 28 h;

[0023] S6). Carry out hot rolling on the homogenized alloy ingot to obtain thin plates;

[0024] S7). Carry out intermediate annealing and cold rolling on the hot-rolled thin plates to obtain Al-Si alloy solder.

[0025] In some examples of the preparation method, the hot rolling inlet temperature is 400 - 420 °C, and the final rolling temperature is greater than 280 °C.

[0026] In some examples of the preparation method, the hot rolling adopts a rolling system with few passes and large reduction, and the reduction rate in the first three passes is ≥55%.

[0027] In some examples of the preparation method, the thickness of the hot-rolled thin plate is 1.5 - 3 mm.

[0028] In some examples of the preparation method, the intermediate annealing is specifically to keep the temperature at 300 - 320 °C for 1 - 1.5 h.

[0029] In some examples of the preparation method, cold rolling is carried out for 3 - 7 passes, and the final thickness is 0.2 - 0.3 mm.

[0030] In some examples of the preparation method, the raw materials include pure aluminum and aluminum master alloy.

[0031] In some examples of the preparation method, the aluminum master alloy is selected from at least one of Al-20Si master alloy, Al-50Cu master alloy, Al-10Ni master alloy, Al-10Cr master alloy, Al-4Be master alloy, Al-4Sb master alloy and Al-5Ti-1Be master alloy.

[0032] In some examples of the preparation method, the hot rolling inlet temperature is 400 - 420 °C, the final rolling temperature is greater than 280 °C, the hot rolling adopts a rolling system with few passes and large reduction, and the reduction rate in the first three passes is ≥55%.

[0033] In some examples of the preparation method, the hot rolling entry temperature is 400 - 420 °C, the finishing rolling temperature is greater than 280 °C. The hot rolling adopts a rolling system with few passes and large reduction per pass. The reduction rate in the first three passes is ≥ 55%. The thickness of the thin sheet obtained by hot rolling is 1.5 - 3 mm.

[0034] In some examples of the preparation method, the hot rolling entry temperature is 400 - 420 °C, the finishing rolling temperature is greater than 280 °C. The hot rolling adopts a rolling system with few passes and large reduction per pass. The reduction rate in the first three passes is ≥ 55%. The thickness of the thin sheet obtained by hot rolling is 1.5 - 3 mm. The intermediate annealing is specifically carried out at 300 - 320 °C for 1 - 1.5 h.

[0035] In some examples of the preparation method, the hot rolling entry temperature is 400 - 420 °C, the finishing rolling temperature is greater than 280 °C. The hot rolling adopts a rolling system with few passes and large reduction per pass. The reduction rate in the first three passes is ≥ 55%. The thickness of the thin sheet obtained by hot rolling is 1.5 - 3 mm. The intermediate annealing is specifically carried out at 300 - 320 °C for 1 - 1.5 h. The cold rolling is carried out for 3 - 7 passes, and the final thickness is 0.2 - 0.3 mm.

[0036] The beneficial effects of the present invention are as follows:

[0037] (1) For the Al - Si alloy solder foil in some examples of the present invention, adding a low - melting - point metal element Zn to the traditional Al - Si solder can effectively reduce the melting point of the alloy, lower the actual soldering temperature, reduce the heat input, and reduce the influence of the soldering process on the properties of the base material.

[0038] (2) Adding an appropriate amount of Sb element to the Al - Si alloy can obtain a typical dendritic structure and dot - shaped eutectic silicon particles, which has a modification effect on the aluminum - silicon alloy and improves the solder properties.

[0039] (3) For the Al - Si alloy solder foil in some examples of the present invention, adding Be can increase the nucleation rate of the hardening phase. In the cast aluminum - silicon alloy, Si is distributed in the matrix as the second phase. The linear expansion coefficients of Al and Si are different. When the casting cools, the α - Al matrix is subjected to the shrinkage tensile stress of the second phase Si with a smaller linear expansion coefficient, and the strain generated cannot be released in time. Many dislocations are generated in the matrix around the Si phase, becoming ideal traps for excess vacancies. Be combines with vacancies to form Be - vacancy pairs and is dissolved in the matrix. Due to the high binding energy between Be and vacancies, the migration of vacancies is effectively blocked, and it becomes the nucleation core of a stable metastable phase, improving its dispersion degree. At the same time, Be can improve the thermal stability of the dispersed phase and the coherent relationship with the matrix, improving the strength of the Al - Si alloy solder.

[0040] (4) Add an appropriate amount of Ni element to replace part of the Cu element in the θ-Al2Cu phase, promote the transformation of the coarse and brittle θ phase from a massive shape to a lamellar shape, promote the uniform distribution and densification of the θ phase, and improve the mechanical properties and corrosion resistance of the solder.

[0041] (5) Intermetallic compounds will form at the interface of the reaction zone of the brazed joint, and their shape, type, and quantity affect the mechanical properties of the joint. In the Al-Si alloy solder foils of some examples of the present invention, during the brazing of 5000 series aluminum alloys, the Mg element in the base material will diffuse into the solder and react with the Si in the solder to form the Mg2Si phase, and its morphology and distribution affect the performance of the brazed joint. The combined addition of Be and Sb can improve the morphology of Mg2Si. The Sb element and the Mg element diffused into the reaction zone will combine to form Mg3Sb2 particles, providing nucleation sites for the crystallization of the Mg2Si phase and reducing the size of the Mg2Si phase. After adding the Be element, Be tends to adsorb on the {100} crystal plane of the Mg2Si phase and combine with Mg atoms, inhibiting the growth of the Mg2Si phase along the <100> crystal direction, and transforming the Mg2Si phase from a needle-like and dendritic shape to a regular massive shape. It is found that the combined addition of Be and Sb in a 2Be-Sb ratio can significantly improve the morphology of the Mg2Si phase at the interface of the brazed joint and significantly increase the strength of the brazed joint. Description of the Drawings

[0042] Figure 1 is the microstructure diagram of the Al-Si alloy solder foil prepared by using Example 2.

[0043] Figure 2 is the shear strength result diagram of the brazed joints of 5052 aluminum alloy brazed with the Al-Si alloy solder foils prepared by using Examples 1, 2, and 3 at 570 °C.

[0044] Figure 3 is the microstructure diagram of the brazed joint of 5052 aluminum alloy brazed with the Al-Si alloy solder foil prepared by using Example 2.

[0045] Figure 4 is the SEM image of the Mg2Si particles in the brazed joint of 5052 aluminum alloy brazed with the Al-Si alloy solder foil prepared by using Example 2.

[0046] Figure 5 is the EDS mapping result of the Mg2Si particles in the brazed joint of 5052 aluminum alloy brazed with the Al-Si alloy solder foil prepared by using Example 2. Detailed Embodiments

[0047] The present invention will be further described below in conjunction with the embodiments, but is not limited thereto. For the convenience of comparison, in each embodiment, the rolling passes are all:

[0048] Hot rolling: 28mm→21mm→16mm→12mm→9mm→6mm→4mm→2mm

[0049] Cold rolling: 2mm→1.1mm→0.6mm→0.3mm→0.25mm→0.2mm.

[0050] The raw materials or master alloys used include but are not limited to pure aluminum, Al-20Si master alloy, Al-50Cu master alloy, Al-10Ni master alloy, Al-10Cr master alloy, Al-4Be master alloy, Al-4Sb master alloy and Al-5Ti-1Be master alloy.

[0051] Refining agents and degassing agents utilize the wettability of their components and aluminum inclusions, as well as the formation of bubbles when certain compounds react in high-temperature molten aluminum, to remove impurities and gases from the molten aluminum, further reducing the impurities in the alloy. This can be achieved using commercially available refining agents. Specifically, the multi-component refining agent and degassing agent are commonly used in the field, including a NaCl-KCl composite refining agent and a C2Cl6 degassing agent. The mass ratio of the composite refining agent to the smelting ingredients is 2:100. The multi-component composite refining agent comprises: 20wt% NaCl, 20wt% KCl, 35wt% NaF, and 25wt% LiF. The mass ratio of the degassing agent to the smelting ingredients is 1:100. After degassing, the molten aluminum is skimmed using a slag skimmer. The skimmed liquid must be centrally processed. When the raw materials are of low purity and contain a high concentration of impurities, the dosage of the multi-component refining agent and degassing agent may need to be increased appropriately.

[0052] Example 1

[0053] 1) According to the weight percentage of the constituent elements, Si: 11.40 wt%, Zn: 10.00 wt%, Cu: 1.25 wt%, Cr: 0.20 wt%, Ni: 0.15 wt%, Mn: 0.13 wt%, Be: 0.42 wt%, Sb: 0.22 wt%, Ti: 0.10 wt%, and the balance is Al; pure Al is smelted in a smelting furnace at a smelting temperature of 750° C. until it is melted; the temperature of the molten aluminum is lowered to 730° C., an intermediate alloy is added, and all of the aluminum is melted; a multi-component refining agent and a degassing agent are added, and the aluminum is refined, degassed, and deslagging is performed, and the aluminum is allowed to stand for 20 minutes; the temperature is lowered to 710° C., the slag is skimmed, and the aluminum is poured into a metal mold preheated to about 200° C. to obtain an alloy ingot;

[0054] 2) homogenizing the ingot at a temperature of 470°C for 24 hours;

[0055] 3) Foil making: The homogenized ingot is subjected to hot rolling-intermediate annealing-cold rolling, wherein the hot rolling temperature is 410°C, the final rolling temperature is 300°C, and the intermediate annealing system is 300°C for 1 hour. The final thickness of the solder foil is 0.2 mm.

[0056] Example 2

[0057] 1) According to the weight percentage of the constituent elements, Si: 12.00 wt%, Zn: 10.00 wt%, Cu: 1.10 wt%, Cr: 0.25 wt%, Ni: 0.20 wt%, Mn: 0.15 wt%, Be: 0.55 wt%, Sb: 0.30 wt%, Ti: 0.10 wt%, and the balance is Al; pure Al is smelted in a smelting furnace at a smelting temperature of 760° C. until it is melted; the temperature of the molten aluminum is lowered to 740° C., an intermediate alloy is added, and all of the aluminum is melted; a multi-component refining agent and a degassing agent are added, and the mixture is refined, degassed, and deslagging is performed, and the mixture is allowed to stand for 20 minutes; the temperature is lowered to 700° C., the slag is skimmed, and the mixture is poured into a metal mold preheated to about 250° C. to obtain an alloy ingot;

[0058] 2) homogenizing the ingot at a temperature of 465°C for 25 hours;

[0059] 3) Foil making: The homogenized ingot is subjected to hot rolling-intermediate annealing-cold rolling, wherein the hot rolling temperature is 400°C, the final rolling temperature is 285°C, and the intermediate annealing system is 3000°C for 1 hour. The final thickness of the solder foil is 0.2 mm.

[0060] Example 3

[0061] 1) According to the weight percentage of the constituent elements, Si: 12.50 wt%, Zn: 11.00 wt%, Cu: 1.30 wt%, Cr: 0.20 wt%, Ni: 0.17 wt%, Mn: 0.10 wt%, Be: 0.50 wt%, Sb: 0.27 wt%, Ti: 0.15 wt%, and the balance is Al; pure Al is smelted in a smelting furnace at a smelting temperature of 750° C. until it is melted; the temperature of the molten aluminum is lowered to 730° C., an intermediate alloy is added, and all of the aluminum is melted; a multi-component refining agent and a degassing agent are added, and the mixture is refined, degassed, and deslagging is performed, and the mixture is allowed to stand for 20 minutes; the temperature is lowered to 710° C., the slag is skimmed, and the mixture is poured into a metal mold preheated to about 200° C. to obtain an alloy ingot;

[0062] 2) homogenizing the ingot at a temperature of 480°C for 24 hours;

[0063] 3) Foil making: The homogenized ingot is processed by hot rolling - intermediate annealing - cold rolling. The hot rolling inlet temperature is 420 °C, the final rolling temperature is 300 °C, the intermediate annealing regime is holding at 320 °C for 1.5 h, and the final thickness of the solder foil is 0.2 mm.

[0064] Comparative Example 1

[0065] 1) Take Si: 12.50 wt%, Zn: 11.00 wt%, Cu: 1.30 wt%, Cr: 0.20 wt%, Ni: 0.17 wt%, Mn: 0.10 wt%, Ti: 0.15 wt% according to the weight percentage of the constituent elements, and the balance is Al; melt pure Al in a melting furnace at a melting temperature of 750 °C until it is completely molten; lower the temperature of the molten aluminum to 730 °C, add master alloy, and melt completely; after adding a multi-component refining agent and a degassing agent, refine, degas and remove slag, and then stand for 20 min; cool down to 710 °C, skim the slag, and pour it into a metal mold preheated to about 200 °C to obtain an alloy ingot;

[0066] 2) Homogenize the ingot at a homogenization temperature of 480 °C for 24 h;

[0067] 3) Foil making: The homogenized ingot is processed by hot rolling - intermediate annealing - cold rolling. The hot rolling inlet temperature is 420 °C, the final rolling temperature is 300 °C, the intermediate annealing regime is holding at 320 °C for 1.5 h, and the final thickness of the solder foil is 0.2 mm.

[0068] Comparative Example 2

[0069] 1) Take Si: 12.50 wt%, Zn: 11.00 wt%, Cu: 1.30 wt%, Cr: 0.20 wt%, Ni: 0.17 wt%, Mn: 0.10 wt%, Be: 0.70 wt%, Sb: 0.1 wt%, Ti: 0.15 wt% according to the weight percentage of the constituent elements, and the balance is Al; melt pure Al in a melting furnace at a melting temperature of 750 °C until it is completely molten; lower the temperature of the molten aluminum to 730 °C, add master alloy, and melt completely; after adding a multi-component refining agent and a degassing agent, refine, degas and remove slag, and then stand for 20 min; cool down to 710 °C, skim the slag, and pour it into a metal mold preheated to about 200 °C to obtain an alloy ingot;

[0070] 2) Homogenize the ingot at a homogenization temperature of 480 °C for 24 h;

[0071] 3) Foil production: The homogenized ingot is processed by hot rolling - intermediate annealing - cold rolling. The hot rolling inlet temperature is 420 °C, the final rolling temperature is 300 °C, the intermediate annealing regime is holding at 320 °C for 1.5 h, and the final thickness of the filler metal foil is 0.2 mm.

[0072] Figure 1 It is the SEM image of the Al - Si alloy filler metal foil prepared in Example 2. It can be seen from the figure that the microconstituents of the filler metal are the Al - Si eutectic phase and the Al2(Cu, Ni) phase. Adding Cu element to the Al - Si alloy can form the θ(Al2Cu) phase, which plays a role in solid solution strengthening and dispersion strengthening, improving the alloy strength. A small amount of Ni element is added to replace part of the Cu element in the θ(Al2Cu) phase, changing the morphology of the brittle phase θ(Al2Cu), making the brittle phase Al2Cu in a lamellar shape, so as to improve the corrosion resistance of the filler metal and the mechanical properties of the joint.

[0073] The 5052 aluminum alloy is brazed using the Al - Si alloy filler metal foils of each example, and the brazing process is 570 °C with a holding time of 10 min. The shear strength test results of the brazed joints of Examples 1 - 3 and Comparative Examples 1 - 2 are as Figure 2 shown. The shear strength of the brazed joint can reach 147.2 MPa.

[0074] Figure 3 It is the microstructural morphology diagram of the brazed joint in Example 2, and short rod - shaped and polygonal Mg2Si phases are observed.

[0075] Figure 4 It is the micro - morphological diagram of the brazed joint in Comparative Example 1, and long fibrous Mg2Si phases are observed.

[0076] High - magnification observation and EDS analysis are carried out on the Mg2Si phase, and Mg3Sb2 particles ( Figure 5 ) are found inside the massive Mg2Si phase. This shows that Sb element preferentially forms Mg3Sb2 particles in the brazing reaction zone. During the solidification of the filler metal, Mg3Sb2 particles first precipitate at the interface. As the temperature decreases, these dispersed particles will become the heterogeneous nuclei of Mg2Si particles, thus promoting the formation of fine and dispersed Mg2Si particles. Since the atomic mass of Be is relatively small, it cannot be detected by EDS energy spectrum analysis. However, according to the first - principle calculation, Be can adsorb on the {100} crystal plane of the Mg2Si phase, promoting the growth of the Mg2Si phase into a regular octahedral morphology.

[0077] The above is a further detailed description of the present invention, and it should not be regarded as a limitation to the specific implementation of the present invention. For those of ordinary skill in the technical field to which the present invention belongs, simple deductions or replacements without departing from the concept of the present invention are within the protection scope of the present invention.

Claims

1. An Al-Si alloy filler metal, with the following mass composition: Si 11.0 - 13.0%, Zn 9.0 - 11.0%, Cu 0.80 - 1.30%, Cr 0.15 - 0.25%, Ni 0.10 - 0.30%, Mn 0.10 - 0.15%, Be 0.40 - 0.60%, Sb 0.20 - 0.30%, Ti 0.10 - 0.15%, and the balance being aluminum and unavoidable impurities.

2. The Al-Si alloy filler metal according to claim 1, wherein, The mass ratio of Be / Sb is (1.7 - 2.3):

1.

3. The Al-Si alloy solder according to claim 1 or 2, characterized in that, The content of the unavoidable impurities does not exceed 0.1%.

4. A preparation method of an Al-Si alloy solder, characterized in that, The composition of the Al-Si alloy filler metal is as described in any one of claims 1 - 3, and it includes the following steps: S1) Weigh the raw materials according to the composition ratio of the Al-Si alloy filler metal, clean and dry them for standby. S2) Transfer the raw materials into a melting furnace, heat and melt them, with the melting temperature being 730 - 760°C. After slag removal, stir evenly. S3) Add a refining agent. After refining, remove the slag and let it stand for filtration. S4) Wait for the molten liquid to cool to 690 - 710°C and pour it into a metal mold preheated to 200 - 250°C to obtain an alloy ingot. S5) Anneal the alloy ingot homogenously at 470 - 490°C for 24 - 28 h. S6) Perform hot rolling on the homogenized alloy ingot to obtain a thin plate with a thickness of 1.5 - 3 mm. S7) Perform intermediate annealing and cold rolling on the hot-rolled thin plate to obtain the Al-Si alloy filler metal.

5. The preparation method according to claim 4, characterized in that, The entry rolling temperature for hot rolling is 400 - 420°C, and the final rolling temperature is greater than 280°C.

6. The preparation method according to claim 4, characterized in that, Hot rolling adopts a rolling system with few passes and large reduction ratios, and the reduction ratio in the first three passes is ≥55%.

7. The preparation method according to claim 4, characterized in that, The intermediate annealing is specifically carried out by maintaining the temperature at 300 - 320°C for 1 - 1.5 h.

8. The preparation method according to claim 4, wherein Cold rolling is carried out for 3 - 7 passes, and the final thickness is 0.2 - 0.3 mm.

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